A SEARCH FOR DENSE GAS IN QUIESCENT BOK GLOBULES

This study demonstrates crucial differences between quiescent Bok glob ules and dark cloud cores. Seventeen small, quiescent Bok globules wer e probed for the molecular lines of NH3 (J, K = 1, 1) and HC3N (J = 4 --> 3) using the Haystack telescope. The spectra have 3 sigma integrat ed line intensity upper limits generally less than 0.1 K km s-1. The u pper limits are less than about 10% of the brightness of TMC-2 in the NH3 (1, 1) line and less than about 30% of the brightness of TMC-2 in the HC3N (4 --> 3) line. Both lower chemical abundances of NH3 and lac k of sufficiently dense gas columns through these globules are respons ible for the absence of detectable lines. A simple statistical equilib rium analysis suggests that these globules have mean volume densities and NH3 abundance factors of 4-5 lower than seen in dark cloud cores. Our upper limits do not require lower than normal HC3N abundances.